Structural features in a brittle-ductile wax model of continental extension

Structural features produced during the rifting of continents depend on the layered rheological properties of the crust and lithosphere and, in particular, on the presence of any transitions between brittle and ductile behaviour(1). Here we use a wax model to explore the gross structural response of continental lithosphere under pure shear extension in the presence of a continuous brittle-ductile transition. The wax models were deformed under various boundary conditions to reflect a variety of different regions, most notably the Basin and Range province of North America. Our experiments show the development of listric normal faults, structures common to regions of continental extension. We also observe the formation of distributed and discrete rifting, and intrusion and occlusion of the upper brittle layer by the ductile lower layer. The factor controlling deformation style in each case appears to be the relative thickness of the brittle and ductile layers, although a relatively high rate of strain generally promotes discrete rifting.